Thank you for your very interesting contributions to this thread @scaron and @jbeale!
Those are indeed the tracks of the pressure wave that was released during the violent explosion of the Hunga Tonga-Hunga Ha’apai. I have seen the same tracks on more than 15 BOOMs and SBOOMs around the Shake network!
Yes, the wave has now passed Iceland, and it should be detected in the coming hours in the UK too. It seems that its magnitude has decreased compared to the one that can be seen on closer weather stations, but we will see.
EDIT: Here’s the infrasound low-frequency signal incoming at my Shake&Boom!
Same here, near Seattle, WA. On my RS&Boom, I got this irregular HDF signal, starting around 5am Pacific time, peaking around 5:15-5:45 lasting almost an hour, then less of a pronounced signal. Is this from the explosion, or the tsunami?
I was interested to see pressure peak on my weather station barometer around 4:30 PST happened about 45 minutes before the peak of the more spread-out infrasound noise at 5:15 PST or 1315 UTC. I wonder if the simple pressure peak is the only thing that really travelled from the volcano, but that drives local air turbulence around any local topography, that causes infrasound afterwards?
On my BOOM that sits rather suboptimally indoors in my basement, I see the infrasound hitting twice as would be expected after travelling almost halfway round the planet to my station in Germany.
Someone should do an animation of the wave propagating thru the BOOM network perhaps.
Looking at my home weather station, I saw a positive pressure spike of 1.2 mbar lasting 35 minutes, peaking at 12:27 UTC (4:27 am PST). Just at the rising edge of that spike (12:10 UTC), there was a 6 mph gust of wind from an unusual direction. My weather station only samples at 5 minute intervals. I note that this pressure peak was much shorter, and about 45 minutes before the infrasound peak measured at the same location (near Portland OR). I’m tempted to speculate the pressure pulse was more about the initial eruption total gas volume and temperature, while the infrasound was about convection cells and turbulence in the developing and more extended volcanic plume.
I saw the same pressure peak here in Sweet Home OR on my Davis weather station. Went back and looked for it after seeing that it was observed by others. I’m sampling at 5 minute intervals. Coincidence or not, with no other rain, my rain gauge bucket decided to tip at the same time. no other rain for ± 10 hrs.
The USGS shared this of the first and second waves from the Cascades:
It’s coming around for another pass!
Shown are the unfiltered infrasound records from Mount Hood, Mount St. Helens, and Mount Rainier. The first signal, appearing at the start of the record (noted by the red box), is the initial airwave from yesterday’s eruption Hunga Tonga-Hunga Ha’apai volcano in Tonga. The second longer but lower-magnitude signal that shows up later in the plot (noted by the gold box) is the airwave passing by the station again! That’s right, the airwave is doing a second lap! The first wave traveled a distance of ~8500 km (~5300 miles). The second traveled ~32,500 km (20,200 miles)! The second pass contains some low frequencies, so might have been detected by barometers, just like the initial airwave.
May have just caught the second lap of the pressure wave from the west in Arizona- The speed of the waves coming from both sides past me worked out to about 720mph, a full lap of the Earth at that speed is around 35 hours, and 4pm MST was about 35 hours since the first pulse hit here at 5am Jan 15th. Timing is right!
I seem to have recorded something again. It is also seen on two other Southern California Booms. No wind at the time. Possibly the opposite direction wave, but the timing does not seem to match up with this info: https://twitter.com/burgwx/status/1482732634077732868
Haven’t seen any noticeable infrasound readings past the initial wave coming from the opposite direction, but the pressure bumps continue. The second lap of the wave from the west arrived in 35 hours, about 36 hours past the wave from the east there was another conspicuous blip- a bit slower but that would still be around 700 mph around the world. I was waiting for it too, it was dead calm and clear outside, nothing else changed
I’ve read they measured Krakatoa’s blast lapping the world 7 times (4 one way, 3 the other), that was with 1880’s gear. These modern readings are already tinier than I think you could sus out of a traditional barograph, but dunno
I was able to detect the second arrivals of the two waves too on my weather station barometer, but the infrasound data did not display relevant signals, especially if compared to the evident arrival of the first two waves.
Waiting for the fifth and sixth arrivals here around 6 pm this evening and during nighttime, but I feel that these should be harder to detect, since the original wave is dissipating. Curious to see what will be recorded anyway.
Hmmm… I kind of doubt this. Your plot is from a seismic sensor, and the event happend at ca 04:15 UTC that day. Seismic waves would reach Germany already roughly 20 minutes later. This was a 5.8 mag earthquake, and it is not totally crazy to think a RS might be able to pick it up. But propagation of sound waves happens much slower but by the time the infrasound reaches Germany, it shoud be so weak that it doesn’t couple into the geophone enough to show up there as a significant event (and it’s not supposed to do that). Also it looks like the infrasound reached Germany later than 18:30 UTC that day, e.g. see my plots. So whatever it is in your plots, it is too late to a be seismic signal from that event and too early to be induced by the sound waves, IMHO.
Right?
HBE
EDIT: also note that the time at the beginning of the plot is 17:30 UTC, not 18:30 UTC . It’s really too early to match observations of the infrasound detections in Germany.
You are probably right HBE. Times to not match. I will dig into this further. It`s my first significant event to analyse. Thanks for the hints!! Helps me building up knowledge.
To quickly spot strong events just by eye (works both for seismic and sonic data…so I’m not completely off-topic here…) you can go to https://stationview.raspberryshake.org , pick your station, click on “24 hour plot” in the station info box on the left hand side and this gets you to a web application that looks a lot like SWARM. The advantage of this is that you can apply a filter to the 24 h data view (use the setting icon on the top right and the “filter” symbol below it to toggle the filter ion and off). For seismic data, a band filter from 0.1 to 1.5 Hz works well in many situations. Strong events will then stand out very clearly in your data, e.g. the screenshot is showing filtered data of your station from 11th of Jan. It detects a strong EQ near Cyprus (highlighted in zoom window) and another one near Alaska later that day around noon.
I’m not so sure what the best filter settings would be for typical infrasound events, but maybe others here can comment on this.
